A PVOH-based resin is excellent in water solubility, solvent resistance, gas barrier property, strength, transparency, hydrophilicity and the like and is used for various applications such as article packaging. Usually, a PVOH-based resin has a melting point and a thermal decomposition temperature close to each other, and in the case of obtaining a molded article, particularly a film or the like, by melt processing, the molding must be performed at a temperature near the decomposition temperature and this causes a problem in the appearance (mixing of an extraneous substance due to burnt deposit or thermal decomposition product) or long-run processability.
As a PVOH-based resin capable of melt processing, an ethylene-vinyl alcohol copolymer reduced in the melting point by ethylene modification is known, but this is not water-soluble and cannot avoid impairment of gas barrier property. As another PVOH-based resin capable of melt processing, a PVOH-based resin having a 1,2-diol component in the side chain has been proposed (Patent Document 1). This PVOH-based resin having a 1,2-diol component in the side chain is reduced in the melting point while keeping water solubility or gas barrier property and can be molded at a low temperature, so that thermal decomposition during melt processing can be suppressed and a molded article with good appearance free from generation of a burnt deposit, a gel and a fish eye can be obtained.
However, although thermal melt processing is possible for the PVOH-based resins, despite capability of hot melt processing, such PVOH-based resins have problem, that when the molding in the melt processing is performed at a high temperature, particularly 200° C. or higher, the molded article tends to be colored and the viscosity of the resin in the melted state increases with time. Therefore, there is a room for further improvements.